LibJS: Add initial implementation for SharedArrayBuffer

None of the actual sharing is implemented yet, but this is enough for
most basic functionality.

Diff Tests:
    +260 ✅    -262 ❌   +2 💀

Userland/Libraries/LibJS/Runtime/SharedArrayBufferConstructor.cpp

@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2023, Shannon Booth <shannon.ml.booth@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/TypeCasts.h>
+#include <LibJS/Forward.h>
+#include <LibJS/Runtime/ArrayBuffer.h>
+#include <LibJS/Runtime/Error.h>
+#include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/SharedArrayBufferConstructor.h>
+#include <LibJS/Runtime/TypedArray.h>
+
+namespace JS {
+
+SharedArrayBufferConstructor::SharedArrayBufferConstructor(Realm& realm)
+    : NativeFunction(realm.vm().names.SharedArrayBuffer.as_string(), realm.intrinsics().function_prototype())
+{
+}
+
+ThrowCompletionOr<void> SharedArrayBufferConstructor::initialize(Realm& realm)
+{
+    auto& vm = this->vm();
+    MUST_OR_THROW_OOM(NativeFunction::initialize(realm));
+
+    // 25.2.4.2 SharedArrayBuffer.prototype, https://tc39.es/ecma262/#sec-sharedarraybuffer.prototype
+    define_direct_property(vm.names.prototype, realm.intrinsics().shared_array_buffer_prototype(), 0);
+
+    // 25.2.4.4 SharedArrayBuffer.prototype [ @@toStringTag ], https://tc39.es/ecma262/#sec-sharedarraybuffer.prototype.toString
+    define_native_accessor(realm, vm.well_known_symbol_species(), symbol_species_getter, {}, Attribute::Configurable);
+
+    define_direct_property(vm.names.length, Value(1), Attribute::Configurable);
+
+    return {};
+}
+
+// 25.2.2.1 SharedArrayBuffer ( length ), https://tc39.es/ecma262/#sec-sharedarraybuffer-length
+ThrowCompletionOr<Value> SharedArrayBufferConstructor::call()
+{
+    auto& vm = this->vm();
+
+    // 1. If NewTarget is undefined, throw a TypeError exception.
+    return vm.throw_completion<TypeError>(ErrorType::ConstructorWithoutNew, vm.names.SharedArrayBuffer);
+}
+
+// 25.2.2.1 SharedArrayBuffer ( length ), https://tc39.es/ecma262/#sec-sharedarraybuffer-length
+ThrowCompletionOr<NonnullGCPtr<Object>> SharedArrayBufferConstructor::construct(FunctionObject& new_target)
+{
+    auto& vm = this->vm();
+
+    // 2. Let byteLength be ? ToIndex(length).
+    auto byte_length_or_error = vm.argument(0).to_index(vm);
+
+    if (byte_length_or_error.is_error()) {
+        auto error = byte_length_or_error.release_error();
+        if (error.value()->is_object() && is<RangeError>(error.value()->as_object())) {
+            // Re-throw more specific RangeError
+            return vm.throw_completion<RangeError>(ErrorType::InvalidLength, "shared array buffer");
+        }
+        return error;
+    }
+
+    // 3. Return ? AllocateSharedArrayBuffer(NewTarget, byteLength).
+    return *TRY(allocate_shared_array_buffer(vm, new_target, byte_length_or_error.release_value()));
+}
+
+// 25.2.3.2 get SharedArrayBuffer [ @@species ], https://tc39.es/ecma262/#sec-sharedarraybuffer-@@species
+JS_DEFINE_NATIVE_FUNCTION(SharedArrayBufferConstructor::symbol_species_getter)
+{
+    // 1. Return the this value.
+    return vm.this_value();
+}
+
+}